1. Field of the Invention
The present invention relates to a bearing mechanism using fluid dynamic pressure. The bearing mechanism is used, for example, in a motor.
2. Description of the Related Art
Some known bearing mechanisms used in motors use fluid dynamic pressure. Such a bearing mechanism is described, for example, in JP-A 2007-100802. In this bearing mechanism, a sleeve is accommodated in a housing. The housing of the bearing mechanism described in JP-A 2007-100802 is a molded article produced by an injection molding process using a resin and molds which can be separated from each other in an axial direction. A parting line of the housing is defined in an outer circumferential surface thereof within an axial range within which neither a tapered surface where an oil surface of a lubricating oil is defined nor a surface to which a holding member is fixed exists.
In the case where a seal portion where a surface of a lubricating oil is located is defined in a seal gap between an outer circumferential surface of a first tubular portion and an inner circumferential surface of a second tubular portion concentric with the first tubular portion, the outer circumferential surface of the first tubular portion includes an inclined portion where the outside diameter of the first tubular portion gradually decreases along the axial direction from a point at which the first tubular portion has the greatest outside diameter. In the case where the first tubular portion having the above structure is molded by using an upper mold and a lower mold which are separated in the axial direction, a parting line is defined in the vicinity of the point at which the first tubular portion has the greatest outside diameter. In this case, depending on design of the upper and lower molds, an air bubble in the lubricating oil may easily stay in the vicinity of the point at which the first tubular portion has the greatest outside diameter in the bearing mechanism.